The Vulptices are foxes with a crstyallin hide and appear to be partially transulcent. They appear to partially domesticated by the Resistance as they are shown running for cover into a Resistance base on the planet.

Rian Johnson has confirmed that the Vulptices are crstyallin and not ice. They live on the planet of the Crait where there is an old Rebellion/ Resistance base. The creatures appear to be mostly wild but also potentially are partially domesticated by the resistance They have borrowed into crevasses inside the old base. The creatures are said to have acquired their crstallin appearance from consuming material from the planet and overtime the subtances of the planet giving them a crystallin bodies.

In EW Star Wars creature workshop Head Neal Scanlan was interviewed

“The idea is that these wonderful sort of feral creatures had lived on this planet and had consumed the planet’s surface, and as such had become crystalline. They live within the burrows and within the tunnels beneath the planet, so there is a time where their ability to shine within the darkness, should provide a guiding light to our heroes.”

Porg Store:
Porgs have already become one of the major hits of a Last Jedi. Many people are snatching up Porg Funko figures and Porg plushy stuffed animals.